1. Technical Field
The present invention relates to a method of printing continuous paper using a line printer that prints to continuous paper using a head unit having a plurality of line printheads disposed with a specific gap therebetween in the paper conveyance direction, and to a line printer that prints to paper using this method.
2. Related Art
Line printers having inkjet line heads that are disposed at a specific interval along the conveyance direction of the continuous paper and eject different colors of ink are one type of printer used for color printing on continuous paper. Japanese Unexamined Patent Appl. Pub. JP-A-2010-234735 describes an ink ejection device that has an inkjet line head.
This type of line printer can perform the printing operation while continuously conveying continuous paper in the conveyance direction during continuous printing, an operation that continuously prints the same content. However, when printing a single print job of a specific length (such as one page) in response to a request from a host computer, an operation that reverses the continuous paper before printing starts to set the position on the continuous paper where printing starts to the printing position of the last of the plural inkjet line heads in the conveyance direction is required. This continuous paper reversing operation is described in FIG. 10 of JP-A-2010-234735.
FIG. 6 describes the need for this continuous paper reversing operation in a line printer having a plurality of inkjet line heads. For ease of understanding, this figure uses label paper having labels of a specific length affixed with a specific gap therebetween to a continuous liner. When a head unit 100 with inkjet line heads for ejecting cyan C, magenta M, yellow Y, and black K ink are used as shown in the figure, and printing one label 102 on the label paper 101 is finished, the trailing end of the label 102 that was printed is at the printing position 104a of the inkjet line head 104 for cyan C at the leading (downstream) end in the conveyance direction 103.
At this time the leading end 108a of the label 108 to be printed next has already passed the printing positions 105a to 107a of the inkjet line heads 105, 106, 107 on the upstream side of the cyan head 104. The label paper 101 must therefore be reversed before printing the next label so that the leading end 108a of the next label is returned to the printing position 107a of the inkjet line head 107 at the trailing (upstream) end of the conveyance direction 103. More specifically, if the distance from the printing position 104a at the downstream end to the printing position 107a at the upstream end is A, and the label gap is B, the label paper 101 must be reversed distance E (=A=B). If the label paper 101 is not reversed, every following label will have an undesirably large top margin.
However, unlike when cut sheet media is reversed, slack equal to the distance reversed will be created when the continuous paper is reversed, and the paper feed path must be configured so that this slack will not create a paper jam. In addition, because continuous paper is typically stored as roll paper wound into a roll, the paper feed load varies greatly due to slack and the inertia of the paper roll, for example, when the paper is then conveyed forward for printing after being reversed. As a result, a precision paper feed mechanism that can convey the paper with good precision without being affected by such load fluctuations is required. Such a paper feed path and paper feed mechanism increase the size and cost of the line printer, and are therefore undesirable.